pucho812

Lost here. Can someone explain why this works
« on: April 25, 2020, 05:44:34 PM »
I am running the following circuit in the link. I have the 24v version and have a wall wart  for the power. If I take 24v from a different source  and apply it to the control pins, it works. The relays will switch and switch back when the control source power  is moved to a different control connection.  But trying to grasp how it is working. While it does the job, why does it do the job?

https://images-na.ssl-images-amazon.com/images/I/A1edk4gzRTL.pdf
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


squarewave

Re: Lost here. Can someone explain why this works
« Reply #1 on: April 25, 2020, 06:24:03 PM »
I don't understand. What exactly are you confused about? You apply a few volts to an input, it turns on the transistor and grounds the relay coil engaging it.

ruffrecords

Re: Lost here. Can someone explain why this works
« Reply #2 on: April 25, 2020, 06:30:23 PM »
Think of the base of the transistor as a dc input rather then an audio one. As long as you apply dc (signal) between the base and ground it will operate the transistor and hence the relay.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

JohnRoberts

Re: Lost here. Can someone explain why this works
« Reply #3 on: April 25, 2020, 06:32:49 PM »
magic?

It is a pretty basic common emitter switch, using a darlington (two transistors in series) switch so very high current gain...  A tiny base current results in a large collector current that saturates the output hard on...

The input has resistor divider network so input voltage (like 5V logic) provides a safe current to the darlington base to turn on the switch..

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

pucho812

Re: Lost here. Can someone explain why this works
« Reply #4 on: April 25, 2020, 06:47:32 PM »
Thanks guys that made more sense.  Cheers.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

pucho812

Re: Lost here. Can someone explain why this works
« Reply #5 on: April 25, 2020, 07:06:22 PM »
What lost me is I am running vcc from a wall wart for this   but getting the 24v for control signal from a different source then the wall wart.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

PRR

Re: Lost here. Can someone explain why this works
« Reply #6 on: April 25, 2020, 08:15:41 PM »
> What lost me is I am running vcc from a wall wart for this   but getting the 24v for control signal from a different source then the wall wart.

All electrons look alike. How can your transistor know where they came from?

My cooling uses a 6V battery to switch a 24VAC relay which switches another 24V relay to clank the contactor and apply 240VAC to the freon squeezer.

squarewave

Re: Lost here. Can someone explain why this works
« Reply #7 on: April 25, 2020, 09:29:55 PM »
What lost me is I am running vcc from a wall wart for this   but getting the 24v for control signal from a different source then the wall wart.
That should be ok but note that it would be very easy to feed a switch 24V through a resistor put a switch on the end and not connect the grounds of two things together unnecessarily. Otherwise, if you're not using a simple switch, just make sure you connect grounds together at the relay module. Presumably the wall-wart ground is floating so it will adjust to match the CV ground just fine. You might want to measure for DC between the grounds just as a sanity check in case neutral is connected to ground and the grounds are off a bit. If they are off even a little you could get some significant current on the ground line which would be bad. Also, if the CV wire is really long (like a few meters or so), you might consider using a shielded cable, add a 100R at the source and a small cap on the relay module input to minimize the possibility of triggering the relay from some kind of EMI like when you flip on a nearby florescent light (although this is almost certainly unnecessary with a bipolar switch). Otherwise, you just need to apply enough voltage to the input to overcome the two diode drops of the darlington albeit through the divider (datasheet says 2.5V).

JohnRoberts

Re: Lost here. Can someone explain why this works
« Reply #8 on: April 26, 2020, 10:43:59 AM »
What lost me is I am running vcc from a wall wart for this   but getting the 24v for control signal from a different source then the wall wart.
That is one of the basic underlying characteristics of digital logic. Your transistor only cares about getting a digital 1, voltage positive wrt ground.  Digital logic is not very picky about how positive or where it comes from (within reason).

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

moamps

Re: Lost here. Can someone explain why this works
« Reply #9 on: April 26, 2020, 03:33:11 PM »
It is a pretty basic common emitter switch, using a darlington (two transistors in series) switch so very high current gain...  A tiny base current results in a large collector current that saturates the output hard on...
I would just add here, if you don't mind, that sometimes using darlington transistor as switching element isn't good idea because the saturation  voltage Vcesat is relatively high (Vcesat(one transistor) + Vbe(second) ) so the disipation on the switching darlington can be substantial.
The voltage loss on darlington transistor can be critical also. For example, it can't be used for switching 3V relays supplied from 3V power supply.   A  singe transistor with Vcesat=0.1V can be used.


JohnRoberts

Re: Lost here. Can someone explain why this works
« Reply #10 on: April 27, 2020, 12:29:19 PM »
I would just add here, if you don't mind, that sometimes using darlington transistor as switching element isn't good idea because the saturation  voltage Vcesat is relatively high (Vcesat(one transistor) + Vbe(second) ) so the disipation on the switching darlington can be substantial.

perhaps TMI but they make and routinely use darlington transitor arrays for GP switching. These are normally expecting 5V logic but the first array I checked will switch 300mA from 3V input and 200mA with 2.4V input.
Quote
The voltage loss on darlington transistor can be critical also. For example, it can't be used for switching 3V relays supplied from 3V power supply.   A  singe transistor with Vcesat=0.1V can be used.
indeed but will require a lower Z input resistor to get enough base current.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

pucho812

Re: Lost here. Can someone explain why this works
« Reply #11 on: April 27, 2020, 02:02:10 PM »
this may be elementary but I'll ask....

Why do they require the input to be up to 24V?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

moamps

Re: Lost here. Can someone explain why this works
« Reply #12 on: April 27, 2020, 04:18:23 PM »
Operating voltage depends of relay's rating and vice versa.
Control input voltage is in ranges
0 to 0,5V for off,
0,5 to 2,5 not defined and
2,5 to 24V for on state.
So you can use any control voltage from 2.5 to 24V for switching relays to on state.

JohnRoberts

Re: Lost here. Can someone explain why this works
« Reply #13 on: April 27, 2020, 05:45:48 PM »
this may be elementary but I'll ask....

Why do they require the input to be up to 24V?
They don't , they accept up to 24v

Some times these auxiliary relays get driven by open collector tallies... a pull up R to 24V supply will work and not exceed input spec.. but that seems arbitrary to not confuse digital engineers...  ::)

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

pucho812

Re: Lost here. Can someone explain why this works
« Reply #14 on: April 28, 2020, 01:19:00 AM »
well wired in and it is working.

nothing gets warm to touch or anything. Everything is grounded to chassis including the the wall wart, PCB grounds are tied together. The input trigger voltage comes from the desk.
The desk had a module in it which was a speaker select module but when they moved the desk from the old location to the new location, the original install techs could not  figure out how to wire it and may have hacked off some critical things.  I have no schematics of that section so I don't know for sure. It has  relays in a card cage that is seperate and the relays are supposed to switch on and off when you hit the buttons on the speaker select module.  for a few years off and on several other techs could't figure it out. At one point the owner was asked to hit up the designer who did all the desk mods and that never happened.    The owner has no idea and would go, it just worked. Famous last words I say.  Through testing I was able to get 24V from the desk down to 1 of 4 eco pins depending on which speaker was selected(mains, mids, small,  smallest), so used that as my input trigger. So far it is working and nothing has blown up or gets hot.   the selects  with new card works. Ha za Ha za. thanks for all the insight and help guys. You are a true delight...
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Phrazemaster

Re: Lost here. Can someone explain why this works
« Reply #15 on: May 05, 2020, 02:52:02 AM »
I remember you showing me that desk Pucho, so kudos for getting this sorted!

Mike
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pucho812

Re: Lost here. Can someone explain why this works
« Reply #16 on: May 05, 2020, 03:46:00 AM »
I remember you showing me that desk Pucho, so kudos for getting this sorted!

Mike
the first design was on vero board and worked ok, but the jbox and switches looked too low fi as you May remember. So a new pcb  that is made elsewhere and wiring to the buttons got it working as intended.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Phrazemaster

Re: Lost here. Can someone explain why this works
« Reply #17 on: May 05, 2020, 05:33:35 AM »
👍🌈
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*********************
******************
***************
************
********
*****
** * Kablooie!


 

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